1. Field of the Invention
The present invention relates to a projection type liquid crystal display (LCD) apparatus and particularly to an LCD unit.
2. Description of the Prior Art
In recent years, optical lifetime of LCD panels and polarizers has become an important factor in proportion as projection type LCD apparatus have been required to have higher brightness and higher contrast. Particularly, when polarizer films (absorptive organic polarizers) have been exposed to intense short-wavelength light in the blue band, they have possibly been burnt by the light. To cope with this problem, there have been developed inorganic polarizers, a typical one of which is a wire grid polarizer manufactured by MOXTEK, Inc. This polarizer is a so-called reflective polarizer that allows transmission of light polarized only in a particular direction and reflects the rest of the light. For this reason, the polarizer has little suffered time degradation due to light irradiation and been used in a projection type LCD utilized for a rear projection TV requiring a longer operating life.
JP-A 2000-356770 discloses an LCD panel provided on the light-incidence side thereof with an absorptive polarizer that is equipped on the light-incidence side thereof with a reflective polarizer.
On the other hand, on the light-emission side of the LCD panel, almost all light that has failed to be transmissive relative to the reflective polarizer, of the light that has been transmissive relative to the LCD panel, is reflected onto the LCD panel when the reflective polarizer has been used without modification. As a result, since a photo-leakage current of a TFT that is a drive element for the LCD panel and polarization disturbance due to multiple reflection of light are induced to obtain an image having insufficient contrast, in general, the reflective polarizer is not used on the light-emission side of the LCD panel. Though it is possible to use the reflective polarizer if the reflective polarizer is disposed at an angle of 45° relative to an optical axis and if an optical configuration in which reflected light is not returned to the LCD panel is adopted, it is necessary to take measures for coping with a large-sized set of complicated configuration and treating unwanted light.
For this reason, as described with reference to FIG. 10 in paragraph [0052] of JP-A 2008-102416, for example, a wire grid is provided on the surface thereof with a light-absorbing layer to form an absorptive polarizer that has come to be used on the light-emission side of an LCD panel.
However, since use of the inorganic polarizer on the light-emission side of the LCD panel causes the degree of polarization to be low as compared with use of the conventional absorptive organic (film) polarizer, the degradation of contrast is induced. Furthermore, in the case of a reflective inorganic polarizer, the light reflected by the polarizer onto the LCD panel as described above and reflected by a metallic thin film that is incorporated into the LCD panel to form a black matrix is irradiated again onto the inorganic polarizer, repeats multiple reflection of light several times and finally enters as unwanted light into the image to be displayed to induce some irregular linear patterns as shown in FIG. 3, thereby deteriorating the picture quality. Incidentally, in FIG. 3, for making it easy to understand where the irregular linear patterns have been induced, a picture-quality black display screen is shown by a gray color to emphatically show the irregular linear patterns. Particularly in the case where an optical compensator is disposed on the light-incidence side of the LCD panel for the purpose of enhancing the contrast or the case where a reflective polarizer is installed on the light-incidence side of the LCD panel, the multiple reflections of light are superposed to considerably deteriorate the picture quality.
In addition, even when the wire grid is provided on the surface thereof with the light-absorbing layer to form the absorptive polarizer, as described above, multiple reflection of light is induced due to a variation in performance of the light-absorbing layer. Empirically, the picture quality is significantly deteriorated if the reflectance is 10% or more.
The present invention has been accomplished in order to solve the problems mentioned above, and the object thereof is to provide an LCD apparatus capable of eliminating the reduction of contrast due to the insufficient degree of polarization of an inorganic polarizer and further eliminating the degradation of a picture quality due to multiple reflection of unwanted light.